Universal Constants
by AllisonWonderland203
Summary: The Doctor considers Rose and all the little ways that she's changed too. Rose x TenToo. Post-Journey's End. Mostly introspective fluff.


**Disclaimer: I own nothing.  
**

The Doctor sat at the kitchen table in their shared flat with his elbows propped up, chin resting in his hands. His newspaper long forgotten, he stared across the table, watching as Rose painted her nails. It was quite domestic, he had to admit, watching her perform such a menial little task, but he was fascinated. Rose bent her head over her hand, using the delicate brush to apply the polish to her fingernails. As she worked, her tongue peeked out of the corner of her mouth.

The Doctor smiled, remembering how many times he'd witnessed this same exact scene on the TARDIS. Before Rose, he'd never had a companion who'd paid so much attention to nail polish. Perhaps it was that she was young or she was trying to stay conscious of her appearance or just plain trying to impress him. It didn't matter now. He'd found her near-obsession with it quite silly, thinking that there was no way one human girl needed _that _many bottles of pink lacquer.

But the color she carefully applied to her fingernails today was dark, a deep shade of plum. She hardly wore nail polish anymore – it wasn't very practical out in the field, where chasing down aliens was far more important than worrying about chipping a nail – but on the few occasions she did, mostly for special occasions such as her mother's party tonight, he'd noticed that she was drawn to darker colors. Gone were the girlish pinks and blues and purples, and in their places were reds, browns, burgundies, and even a chic black.

He watched her layer a coat of polish on her thumb and came to the sudden and shocking realization that Rose was no longer a girl – she was a woman in every respect. She'd grown up.

It seemed stupid to think of it now, of all times. It wasn't the first time he'd realized that during their years apart she'd grown into someone slightly different. Having the privilege of seeing her day in and day out, he caught himself watching her sometimes, as he was doing now, trying to catalogue those differences. Oh, he knew she was probably doing the same to him – and how could she not? His differences were quite obvious – one heart instead of two, a thoroughly human body temperature, an surprising need for regular sleep – but hers were more subtle. Just small things that somehow made her someone different, someone he didn't quite recognize.

He often tried to imagine what that time had been like for her, what had happened to her that caused such a change in her. He knew how difficult it had been to be separated from her. He had felt those same agonizing pangs of loss, but he'd had distractions, the TARDIS, all of time and space. She had had nothing, nothing but this unfamiliar world. He had moved on, hoping to distract himself into forgetting, but she had bravely faced it, day after day, fighting for a way to get back to him. He was a coward every time and she was ever the valiant warrior. His brave girl… No. Not girl – woman now.

He had recognized a change in her from the very first moment he saw her on that dark London street. He'd never thought he'd ever see her again and then, suddenly, there she was – flesh and blood and that smile, always that smile – the same Rose who had haunted his dreams ever since that disastrous day he'd lost her.

She was every bit his Rose, but she was different, having evolved into someone _more. _She carried herself differently, with more purpose than she ever had before. Gone was the flighty, carefree, headstrong teenager he'd first swept into his TARDIS and carried across the galaxy. In her place was a woman, confident and strong. A capable leader who wasn't afraid to take matters into her own hands and stick up so bravely for what she believed in.

She was more serious than he recalled. In the few days he'd spent with her in this universe, the Doctor had noticed something reserved about this Rose that he wasn't sure of. He wondered if the change had to do with her position at Torchwood, that in becoming a respected leader she'd put away some of her more carefree nature and adopted a more professional persona that she carried with her everywhere. Or maybe it was just simply the fact that she was no longer nineteen and carefree. Or maybe – he cringed to consider this – it was the fact that she was no longer innocent, that she had experienced hurt and loss and pain so great that she had shut off a part of herself and kept a tight rein on emotion as not to feel too much. He understood that. He hoped for her sake that she hadn't, but he understood all the same. Yet,_ if_ she had, it was his sincerest wish that maybe now they were together she could start to heal, to learn how to be as happy as they were once upon a time.

There were physical differences, too. She was thinner now. He'd noticed at first a slight leanness to her that had not been present before. Then, when he'd hugged her close, he'd noticed how his arms wrapped around her a little more than they had before, how the sharpness of her shoulder blades was a little more prominent than he remembered. Now, as his eyes roamed over her cheekbones, the thinness in her face, he renewed his promise to himself that he would make sure that she was taking proper care of herself.

Another thing he'd noticed was her hair. It wasn't as blonde as it used to be – no longer peroxide bleach-blonde as it had been in the days she traveled with him – but a more natural, slightly darker color. It wasn't bad – in fact, he thought it made her look more endearing, more _real, _in a way. It was longer too, not by much, but still shorter than it once had been when she'd first stepped foot in the TARDIS. It appeared to be better kept and he wondered how much of that had to do with her role as the daughter of one of the wealthiest men in London.

This Rose also wore less makeup – no more dark eyeliner and heavy mascara. Just simple, clean, and fresh; enough to accentuate without detracting from the beauty she'd always possessed. He'd always thought her beautiful, even when he'd had a manic grin and enormous ears and hadn't quite been sure of himself or the affect that this pink and yellow earth girl she had on him. And, oh, she had an effect on him, more so now than ever before, now that he was half-human and fully able to give him every part of his one heart.

He glanced back up at her face and was startled to find her looking right back at him. She held the little brush poised in her hand, a ghost of a smile playing on her lips. Their eyes remained locked for a long moment, the Doctor unsure of what to do. As his embarrassment deepened, he was afraid a rather unbecoming flush was spreading of his face and neck – curse this human body that felt things so easily and betrayed him so visibly! He opened his mouth as if to explain himself, but she beat him to it

"Don't apologize," she said without preamble, flicking her eyes back to her nails. "I knew you were staring."

He blinked in response, shutting his gaping mouth with a soft click of his teeth. Ever-perceptive, his clever Rose. There was no use denying what she'd obviously caught him doing, so he folded his arms on the tabletop and tried his best to look casual. "Do you mind?"

"Nope." She screwed the cap back on and set the bottle of polish aside. "You just stopped talking all of a sudden and went off into the Twilight Zone or something."

"I was just thinking," he shrugged. "And I'll have you know, there's no such thing as the Twilight Zone. Looked for it for years, never found it. Fascinating television program though."

Rose rolled her eyes at him. "Thinking about what?"

He gestured with his chin to her fingernails. "Your nail polish…"

She glanced down at her fingers and looked back up at him quizzically. "Yeah? What about it?"

"It's nice."

She laughed, shaking her head at him. He wasn't sure what was so funny, he found himself smiling too. Her infectious laugh had that affect on him. That was one thing that hadn't changed in all these years. He prayed it never would.

"You're so weird sometimes. You sure you're okay?" she asked, reaching across the table, hands palm up, open in an invitation.

He took her outstretched hands. He always had and always would. As long as he could take her hand, he would always be all right. He squeezed her hands gently before turning them over and inspecting her freshly-polished fingernails. Beautiful. She always had been and always would be. Forever and ever and ever.

These were the little things he could cling to, that no matter what else happened or how much either of them changed, she would always be beautiful to him, always smile for him, always laugh just like that, and always take his hand and run. Some things changed, because change was always inevitable, but some things were universal constants, even across universes.

The Doctor brought her hands to his lips, placing a kiss on the back of each one before meeting her eyes once more.

"I have you, Rose Tyler," he said softly, "so yes. I'm sure I'm okay."

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